The invention relates to a tape cassette which is used in a magnetic tape recorder, and more particularly, to an improved tape cassette which assures a smooth running of a magnetic tape contained therein.
As is well recognized, a tape cassette which is used in a magnetic tape recorder of the cassette type is provided with a variety of sophistications which are utilized in order to prevent a magnetic tape contained therein from becoming loose or deformed in its winding form, but the prior art approaches failed to provide a satisfactory solution to prevent these undesirable effects completely.
During a rapid advance or rewind mode, the tape runs at a higher speed, which may cause a lateral displacement of the tape, resulting in a deformed or offset or staggered winding. This increases the frictional resistance which the tape experiences during its running, whereby the running performance becomes unstable. In particular, with a tape cassette of a miniature size which is commonly referred to as MICRO-CASSETTE (registered trademark), there is a reduced distance from a point on an associated tape hub where the tape is delivered to a magnetic head, so that the use of tape guides is insufficient to bring the running tape into an optimum record/playback position with respect to the head, as considered in the lateral direction, resulting in the difficulty that the azimuth during the record/playback of the first surface (surface A) of the cassette is offset from that during the record/playback of the second surface (surface B) of the cassette. A support spring which is associated with tape pads is held between a spring abutment and another spring support post, both located within the cassette, and is subject to a degree of rattling in the lateral direction or in the direction of thickness of the tape cassette. Hence, it is impossible to bring and maintain the tape at the optimum record/playback position with respect to the magnetic head by the use of such pads alone.
One of the attempts which intended to eliminate such inconveniences of a conventional tape cassette is disclosed in Japanese Utility Model Publication No. 6358/1975 where ribs are mounted on the inner wall surface of a cassette half. With this arrangement in which no liner sheet is used and the tape bears against the ribs directly which are mounted on the inner surface of the cassette half, a shifting of the tape in the lateral direction during the tape running, in particular, during a rapid advance or rewind mode, is reduced, effectively preventing a deformed winding of the tape. However, the resulting smoothness of tape running is less than that achieved with the use of a liner sheet.
Accordingly, there has been proposed to provide ribs on the internal surface of the cassette half to control the position of a liner sheet so that a deformed winding of the tape may be prevented. Such a tape cassette is illustrated in FIG. 1. As shown, a tape cassette 1 is formed by a pair of upper and lower cassette halves 2, 3 carrying ribs 2a, 3a on their inner surfaces. The provision of such ribs reduces a displacement of the tape in the lateral direction as compared with the tape movement without them, but because the width of tape receiving surfaces of a pair of tape hubs 4, 5 is less than the distance between the aligned ribs 2a, 3a, a lateral displacement of tape hubs may occur depending on the machining accuracy thereof to cause an unstable tape running. A pair of upper and lower liner sheets 7, 8 are provided. Their ends, in particular, those of the upper liner sheet 7, depend downwardly outside the windings of tape 6 which are disposed on the tape hubs 4, 5, so that the edge of the tape 6 may move into contact with the liner sheets 7, 8 as the tape is being taken up on or delivered from the tape hubs 4, 5, resulting in a skewed running of the tape. This results in a deformed winding of the tape 6.
Another tape cassette is disclosed in Japanese Utility Model Publication No. 9000/1975 where a sheet having a low friction surface is disposed for receiving the edge faces of a tape winding disposed within the cassette. A deformation of the sheet is prevented by providing a plurality of projections extending from the inner surface of the cassette casing so that the sheet may be held in planar form parallel to the inner surface of the casing. Even though a number of projections may be provided to maintain the sheet in a plane which is substantially flush with the inner surface of the casing, an inherent deformation of the sheet may cause a skewed tape running and a deformed winding in the similar manner as mentioned above in connection with the tape cassette 1.
Japanese Laid-Open Utility Model Application No. 69,128/1975 discloses a further tape cassette in which a liner sheet extends to a point where it crosses a pad supporting spring. Even with this cassette, it is impossible to eliminate a rattling of the pad spring in the lateral direction perfectly.